The present invention relates to polymeric vesicles formed from polyamino acid derivatives. The polyamino acid is modified so as to bear at least one hydrophilic group and at least one hydrophobic group. Vesicle formation is then induced in the presence of cholesterol. The vesicles are suited for entrapment or conjugation of pharmaceutically active agents, in particular nucleic acids.
The understanding of the human genome has led to a profound appreciation of the genetic basis of diseases such as cancer. The refractory nature of many solid cancers to conventional treatments coupled with the significant ageing of Western population means that fatalities associated with these cancers are likely to rise. Increasingly alternative modes of treatment are being sought, one of which is the use of deoxyribonucleic acid (DNA) as a therapeutic agent. The use of medicinal genes (gene therapy) is exemplified by the administration of prodrugs that are activated by a gene product. The targeting of this gene to tumours will localise therapy to specific areas.
Additionally, the use of gene medicines prophylactically to either add tumour suppressor genes or obscure pathogenic mutations by gene replacement has been advocated. The engineering of the expression of a gene product that stimulates the immune system to destroy cancer cells is another area awaiting exploitation.
Apart from the treatment of solid tumours other incurable genetic diseases such as cystic fibrosis and sickle cell anaemia that typically kill their victims before they reach reproductive age are also likely to benefit from treatment with gene medicines. Cystic fibrosis has received a great deal of attention recently as not only viral but non-viral gene delivery systems have been used experimentally against this disease in the clinic and although gene expression was detected with the use or a non-viral gene medicine, this expression was transient in nature.
Advances in recombinant DNA technology have meant that the development of the active ingredient in gene medicines i.e. the gene itself is now possible. However the delivery of genetic material to the sites of pathology still remains a major hurdle.
Viral gene delivery vectors have been tested and found to give stable expression in the case of adenoviruses. However, adenoviruses precipitate a severe immunological reaction that precludes administration of a repeat dose of the gene.
Retroviruses on the other hand which hold the advantage of preferentially infecting actively dividing cells are more likely to insert DNA in the host genome with unknown consequences.
Non viral gene delivery systems fall in to two broad classes: cationic polymeric systems, incorporating targeting ligands which form a transfection competent ionic complex with the gene of interest and self-assembled cationic amphiphilesxe2x80x94cationic liposomes which form a transfection competent complex between the amphiphilic components of the liposomes and the gene. These systems are found to transfect cells well in culture but in vivo gene expression is very low and of a transient nature.
Polylysine has previously been modified by the attachment of phospholipid groups and used in DNA transfection (Zhou, X H et al (1991) Biochim. Biophys. Acta 1065: 8-14 and Zhou, X h, Huang L (1994) Biochim. Biophys Acta 1189: 195-203).
Polylysine has also been modified by the attachment of hydrophilic groups such as polyethylene glycol (Azinger H, et al 1981) Makromol Chemie-Rapid Commum. 2: 637-640 and Dash P R, et al (1997) J. Contr. Rel. 48: 269-276) and various sugars (Kollen W J W, et al, (1996) Human Gene Ther. 13: 1577-1586 and Erbacher P, et al (1997) Biochimica Biophysica Acta 1324: 27-36).
In addition various drugs (Hudecz F. et al (1993) Bioconjugate chemistry 4: 25-33) and targeting residues such as transferrin (Wagner, E (1994) Adv. Drug Delivery Rev. 14: 113-135), asialoglycoprotein (Chowdhury, N R et al (1993) J. Biol. Chem. 268: 11265-11271) and monoclonal antibodies (Chen, J B et al (1994) Febs Lett 338: 167-169) have been conjugated to polylysine.
FR2574185 relates to lysine polymers intended for use as supports for the preparation of reagents for the diagnosis of haptenic allergies wherein the molecules have the same number of L-lysine radicals between 8 and 20 and have been modified so as to include alternating hydrophilic and hydrophobic substituents.
According to the present invention there is provided a compound which is a derivatised polyamino acid bearing at least one hydrophilic group and at least one hydrophobic group per molecule.
The polyamino acid is preferably a straight chain homo- or heteropolymer joined by amide linkages and may be of natural or synthetic origin. Most preferably the polyamino acid is a straight chain homopolymer. Preferred straight chain homopolymers include poly-L-lysine and poly-L-ornithine, or any other amide linked heteropolymer made from amino acids. The polyamino acid may have a molecular weight of about 600-1,000,000, preferably 15,000-30,000.
Preferably the hydrophilic group is cationic or non-ionic. In one embodiment, DNA is designed to be associated with the compound when assembled as a vesicle. An anionic hydrophilic group would however repel anionic DNA. The hydrophilic group may be selected from hydrophilic drug molecules or ligands, sugars, oligosaccharides, polyhydroxy molecules e.g. sorbitol or various organic groups.
Typical organic groups nay be selected from mono- and oligo-hydroxy C1-6 alkyl, mono- and oligo-hydroxy substituted C2-6 acyl, C1-2 alkoxy alkyl optionally having one or more hydroxy groups substituted on the alkoxy or alkylene groups, oligo- or poly-(oxa C1-3 alkylene) preferably polyoxyethylene comprising up to about 120 ethylene oxide units (i.e. up to a molecular weight of 5000), and C1-4 alkyl (oligo- or poly-oxa C1-3 alkylene) optionally hydroxy substituted preferably oligo- or polyglycerol ethers such as those described in GB-A-1,539,625, for example containing up to 10 glycerol units; and wherein R1 is joined via an amide linkage to an amino acid unit of the polyaminoacid. It is to be understood herein that the term acyl includes alkenoyl and alkynoyl groups as well as alkanoyl groups.
The hydrophobic group may be selected from hydrophobic drugs or ligands, steroid derivatives, hydrophobic macrocyclics or organic chains.
Preferred hydrophobic organic chains include C12-24 alkyl, alkanoyl, alkenyl, alkenoyl, alkynyl or alkynoyl straight or branched chains.
The compound has a degree of substitution by the hydrophilic groups in the range (hydrophilic groups:amino acid monomers) of 1:40-1:1, preferably 1:20-1:2. The compound has a degree of substitution by the hydrophobic groups in the range (hydrophobic groups:amino acid monomers) of 1:20-1:1, preferably 1:10-1:2.
The ratio of substituent hydrophilic:hydrophobic groups in the compounds of this invention is in the range 20:1 to 1:20, preferably 10:1 to 1:10, for example 5:1.
A preferred range of compounds are substituted poly-L-lysines or poly-L-ornithines wherein a free amine of a lysine or ornithine monomer is substituted with mono- or oligo-hydroxy C1-6 alkyl, mono- or oligo-hydroxy substituted C2-6 acyl, C1-2 alkoxy alkyl optionally having one or more hydroxy groups substituted on the alkoxy or alkylene groups, oligo- or poly-(oxa C1-3 alkylene) such as polyoxyethylene comprising up to about 120 ethylene oxide units and C1-4 alkyl (oligo- or poly-oxa C1-3 alkylene) optionally hydroxy substituted such as polyglycerol ethers, for example containing up to 10 glycerol units; and a free amine of a further lysine or ornithine is substituted with C12-24 alkyl, alkanoyl, -alkenyl, alkenoyl-alkynyl or alkynoyl.
Particularly preferred compounds are palmitoyl poly-L-lysine polyethylene glycol (PLP) (see FIG. 1) or palmitoyl poly-L-ornithine polyethylene glycol (POP).
The compounds may be formed by first reacting a polyamino acid with the hydrophilic group followed by reaction with the hydrophobic group.
The compounds described herein are used in combination with cholesterol or a derivative thereof to form vesicles. In the absence or cholesterol, particle formation does not occur and the material precipitates. Consequently, the presence of cholesterol is required to promote self-assembly of the polyamino acids to form vesicles.
The vesicles are made by techniques similar to those used to form liposomes and niosomes, for instance by blending the compounds in an organic solvent and then contacting the dried mixture with an aqueous solution, optionally followed by a particle size reduction step. Alternatively vesicles may be prepared by sonicating a mixture of modified polymers and cholesterol in the presence of an aqueous solvent.
The vesicles formed may be suspended in an aqueous vehicle or alternatively may be freeze-dried. The vesicles may optionally incorporate a steric stabilizer, for instance a non-ionic amphiphilic compound, preferably a poly-24-oxyethylene cholesteryl ether. The vesicles may be in the micron or nanometer size range, nanometer sized vesicles being formed preferably in the presence of the steric stabilizer. In this case, the steric stabilizer is incorporated into the structure of the vesicle.
The vesicles preferably also comprise an associated pharmaceutically active ingredient. The active ingredient may be water soluble, in which case it will be associated with the hydrophilic regions of the particle, or water insoluble and consequently associated with the hydrophobic regions of the particle.
Such an ingredient is preferably physically entrapped within the particle but may also be held by covalent conjugation. The pharmaceutically active ingredient may be a peptide or protein therapeutic compound. A further preferred alternative for the pharmaceutically active compound is nucleic acid (e.g. DNA), preferably in the form of a gene for gene therapy or gene vaccination.
These pharmaceutical carrying vesicles may be used for the treatment of a human or animal by therapy, in particular for oral drug delivery of peptides or proteins or as gene delivery vectors. It is envisaged that this drug delivery system will also be useful when used via the intravenous, intramuscular, intraperitonial or topical (inhalation, intranasal, application to the skin) routes.
Other agents may be included in a pharmaceutical formulation comprising the vesicles of the present invention. Such other agents may include agents which improve the pharmacology of the vesicles such as chloroquine and primary, secondary or tertiary amines.
The pharmaceutical composition may optionally further comprise a pharmacologically acceptable carrier.